1. Field of the Invention
The present invention relates to a refrigerating unit of a binary refrigerating system comprising independent dual refrigerant circuit, wherein an evaporator of a high temperature side refrigerant circuit and a condenser of a low temperature side refrigerant circuit form a thermal exchanger.
2. Description of the Prior Art
The conventional binary refrigerating unit is shown in the Utility Model Publication No. 58-23101. Namely, each refrigerant circuit in the high temperature side and low temperature side comprises independent dual refrigerant closed-circuit, and an evaporator of the high temperature side refrigerant circuit and a condenser of the low temperature side refrigerant circuit form a thermal exchanger so that the refrigerant of the low temperature side refrigerant circuit is condensed by the evaporation of the refrigerant of the high temperature side refrigerant circuit. Thereby, since it is possible to use the refrigerant having lower boiling point (evaporation temperature) to the low temperature side refrigerant circuit, it is possible to obtain an extremely low temperature by the evaporator of the low temperature side refrigerant circuit.
In the above mentioned dual refrigerating system, it is possible to obtain the low temperature about -80.degree. C. in the evaporator of the low temperature side refrigerant circuit normally. However, in order to the lower temperature such as -130.degree. C., it needs to improve the structure of the refrigerant circuit and to add the various kind of modification to the sealing refrigerant composition
The applicant of the present invention disclosed the above mentioned latter method, that is, the way of realizing a super low temperature of -130.degree. C. by improving the sealing refrigerant composition in the specification of the Patent Application No. 61-91599 which was filed prior to the present case.
In detail, R500 or R502 are sealed into the high temperature side refrigerant circuit and R13B1 (bromotrifluoromethane) or R503 are to the low temperature side refrigerant circuit, respectively.
However, according to the above mentioned structure, the refrigerants such as R500, R502, R13B1, and R503 are the refrigerants which are the object of a regulated flon and it has been studied to replace to the refrigerant out of the regulated immediately from the viewpoint of an environmental protection of an ozone layer destroy and so on.
On the other hand, since this refrigerating unit is mainly used for keeping an organism such as blood and an examined body for long time in a biotechnology field, the unit for realizing the lower temperature, for example, -150.degree. C. has been required from the viewpoint of the reliability.